I. Field of the Invention
The present invention relates generally to a portable hole boring machine and, more particularly, to a machine which can be readily mounted on the access to a flow control valve of the class used in industrial pipelines carrying high pressure steam, or the like, for remachining or resurfacing the seal ring seat surface of the valve access when it becomes worn. This is accomplished without having to remove the valve from the pipeline.
II. Discussion of the Related Art
Large industrial pipelines used to transport fluids such as high pressure superheated steam will commonly include valves, including one-way or check valves, for fluid flow control. For example, electric utilities may include such pipelines for routing high pressure steam from a boiler to the turbines used in driving the electric generators. One valve commonly used is the Duo-Chek.TM. manufactured and sold by the Mission Manufacturing Company of Houston, TX. This valve is representative of a type commonly used in such installations. The need to refurbish these valves in more rapid and less expensive manner has created an important impetus for the present invention. Because such is the case, it is believed that a greater understanding of the problem will be helpful and it will next be described in greater detail.
With particular reference to FIGS. 1 and 2, such valves include a valve body 10 having a longitudinal bore 12 formed therethrough. A pair of hinge pins 14 extend transversely across the bore near the inlet end 16 and carry pivotally hinged first and second semi-circular, butterfly-type check valve plates 18 and 20. A spring 22 urges the valve plates to a normally closed, flow blocking or checking position which precludes flow back through the inlet. Of course, when the force on the inlet site exceeds the spring force plus the force exerted by any material downstream of the check valve, plates 18 and 20 are pivoted against the force of the spring 22 so that their planes approach a disposition parallel to the flow direction indicated by the arrow 24. The plates 18 and 20, then, are free to open and close to allow unidirectional flow in response to relative changes in up stream and down stream pressures.
After a period of use, the parts wear and it becomes necessary to service the valve plate assembly to assure continued proper operation. On should bear in mind that the valves and associated piping are normally quite large, i.e., 12 or more inches in diameter and are made of very heavy gauge material. The valve body is normally welded in place in the pipeline; and, therefore, it is difficult and time consuming to remove. The valve is provided with a radially disposed access port shown generally at 26 which addresses the inside of the valve body and allows access to the interior of the valve for repair of the valve plate assemblies in situ. The access port is a mechanical bore 28 of circular cross section of a predetermined precise diameter and normally sealed by a stainless steel plug 30, associated soft iron seal ring 32, a stainless steel spacer ring 34 and a stainless steel retainer ring 36 which fits in the manner of a snap ring into an annular groove 38 formed in the valve body. A circular cover 26 fits into the valve body 10 and bolts 42 pass through the cover into threaded bores in plug 30. As the bolts are drawn tight, the plug 30 is pulled toward the cover to force the seal ring 32 and the spacer ring 34 tightly against the retainer ring 36 to form a high-pressure, gas-tight seal.
With the passage of time, and a workage of erosive or corrosive material such as such high-pressure, superheated steam, the seal ring 32 becomes worn. This further allows fluid under high pressure to erode the cylindrical wall of the bore 28 or seal ring surface of the access port. If unattended, high pressure steam escaping past the seal ring 32 easily scores, i.e., wears grooves in the access bore 28. This is a very common occurrence; however, simple replacement of the valve ring 32 does not adequately reseal the system. Thus, it becomes necessary to remachine or resurface the seating surface of the bore 28 to a new predetermined tight specification allowing a seal ring and spacer ring of a predetermined larger diameter to replace those previously used.
Accordingly, it is the primary object of the present invention to provide a portable boring tool which can be used to refinish the access bore 28 on a valve of the class described in situ.
With further regard to the in situ renovation of the valves, those skilled in the art will appreciate that in many industrial piping systems such as those found in power plants, only limited vertical or radial clearance may be available above the check valve access port; and, hence, there is added difficulty in gaining the necessary clearance to the access port for the use of a vertical milling machine. Moreover, the milling machine must be capable of rigid securement to the valve body with the cutting tool precisely centered and leveled relative to the access bore and valve body if truly concentrical remachining is to be achieved.
It is, thus, another principal object of the present invention to provide a reboring or milling machine which requires little in the way of vertical height and which can easily and rapidly positively position a machining tool with great precision with reference to three mutually perpendicular axes relative to the bore to be resurfaced.
It is further significant that in nuclear power facilities it can occur that a valve must be refurbished in a location where a radiation hazard may exist. As such, to limit human exposure, it is imperative that the setup and removal of the machine be accomplished quickly and that it be capable of operating without human intervention. Prior art equipment used to refurbish DuoChek.TM. valves commonly required total removal of the valve from the pipeline and reboring in a machine shop which required, in turn, prolonged exposure periods for cutting out and later rewelding of the valve into the line. By accomplishing reduction in exposure time for those working on the project, the invention represents much-needed safety step.
The valve seat resurfacing machine of the present invention requires only a fraction of an hour to assemble in position on the valve and to properly center the cutting head. When setup is complete, the machine can run by remote control without need for human intervention. Subsequent removal of the tool and replacement of the new rings and plug the access can also be accomplished in a manner of minutes.